Selective binding of polystyrene particles, gold particles, silver particles, as well as polystyrene particles coupled to gold and silver particles have been used to identify cell types in a laser flow cytometer by light scatter rather than by fluorescence (Bohmer, King. Journal of Immunologic Methods, “Immuno-Gold Labeling for Flow Cytometric Analysis. 74(1984)49-57; Bohmer, King. Cytometry, “Flow Cytometric Analysis of Immunogold Cell Surface Label. 5(1984)543-546; Festin, Bjorklund. Journal of Immunological Methods, “Detection of Triple Antibody-binding Lymphocytes in a Standard Laser Flow Cytometry using Colloidal Gold, Fluorescein and Phycoerythrin as Labels”. 101(1978) 23-28). While a light-scatter laser flow cytometer is simpler, more durable, and significantly less expensive to manufacture than a fluorescence flow cytometer, these prior art light scatter assay methods need several complex user steps or expensive manufacturing steps to enhance the light scatter signal, and create a detectable signal over background light scatter from the cells themselves.
The need for multiple steps by a skilled user and/or the high cost of manufacture, prevents these prior art particle binding assays from being used in resource-poor environments where highly trained laboratory technicians are not widely available, and health care is poorly financed. Within the industrialized nations, eliminating the need for a highly trained laboratory technicians and reduced manufacturing cost is desired for health care cost containment.